katydid-0.3.0.0: src/Exprs/Type.hs

-- |
-- This module contains the Relapse type expression.

module Exprs.Type (
    mkTypeExpr
    , typeExpr
) where

import Expr

-- |
-- mkTypeExpr is used by the parser to create a type expression for the specific input type.
mkTypeExpr :: [AnyExpr] -> Either String AnyExpr
mkTypeExpr es = do {
    e <- assertArgs1 "type" es; 
    case e of
    (AnyExpr _ (BoolFunc _)) -> mkBoolExpr . typeExpr <$> assertBool e;
    (AnyExpr _ (IntFunc _)) -> mkBoolExpr . typeExpr <$> assertInt e;
    (AnyExpr _ (UintFunc _)) -> mkBoolExpr . typeExpr <$> assertUint e;
    (AnyExpr _ (DoubleFunc _)) -> mkBoolExpr . typeExpr <$> assertDouble e;
    (AnyExpr _ (StringFunc _)) -> mkBoolExpr . typeExpr <$> assertString e;
    (AnyExpr _ (BytesFunc _)) -> mkBoolExpr . typeExpr <$> assertBytes e;
}

-- |
-- typeExpr creates an expression that returns true if the containing expression does not return an error.
-- For example: `(typeExpr varBoolExpr)` will ony return true is the field value is a bool.
typeExpr :: Expr a -> Expr Bool
typeExpr e = Expr {
    desc = mkDesc "type" [desc e]
    , eval = \v -> case eval e v of
        (Left _) -> return False
        (Right _) -> return True
}